1. Visible growth — even small.
This is the obvious one. Black, green or grey staining on bathroom ceilings, around windows, in exterior-wall closets, on basement masonry. Visible growth above 10 square feet pushes the project into licensed NYS Article 32 territory regardless of where it sits.
What people miss: stained patches that are old growth, killed by drying, but never removed. Those still produce allergenic fragments and indicate a moisture history worth investigating.
2. A leak history with no follow-through.
Burst supply line two winters ago. The drywall was replaced. Was the cavity inspected? Was the insulation pulled? If the answer is "they said it was fine," an assessment is the cheapest way to confirm.
Hidden growth inside wall cavities is common when wet materials were dried in place rather than removed.
3. Tenant complaints clustering in a single location.
Health complaints from the same line — Apt 4B, 5B, 6B — are an HVAC-or-envelope signal. The shared element is usually a riser, a chase, a roof condition, or a façade detail. The investigation should follow that geometry, not just the unit reporting the loudest complaint.
4. Persistent indoor humidity.
Anything above 60% RH for extended periods will eventually grow mold somewhere — typically on the coolest interior surfaces (closet exterior walls, behind bedroom furniture, around windows). Sustained high indoor humidity in winter usually means too much moisture is being added (cooking, drying, occupancy) for the ventilation rate. In summer it usually means an under-dehumidified envelope.
5. HVAC odor that doesn't clear.
A musty smell when the air handler kicks on, that doesn't dissipate after the fan runs for an hour, often traces back to growth in the coil, drain pan or filter section. This is straightforward to confirm with a brief assessment and addresses a much larger occupant-comfort issue than the visible component might suggest.
What an assessment actually produces.
A NYS Article 32 mold assessment gives you a written report with: moisture mapping, surface and air sampling results from an AIHA-LAP accredited lab, and a remediation work plan — handed to your contractor. The work plan defines scope, containment class and clearance criteria, so the remediation isn't a negotiation later.